How to grade categories of evidence

Figures & data

Table I.  Comparisons of the grading scheme for categories of evidence used by the NICE Guidelines for Anxiety Disorders (Eccles and Mason 2001) with the WFSBP Guidelines system. ¹These standards are defined in Bandelow et al. (2008, this issue).

Eccles and Mason (2001)		World Federation of Societies of Biological Psychiatry (WFSBP)
Category of evidence	Description	Category of evidence	Description
I	Evidence from: meta-analysis of randomised controlled trials, or at least one randomised controlled trial	↑? A	Full Evidence From Controlled Studies is based on: two or more double-blind, parallel-group, randomized controlled studies (RCTs) showing superiority to placebo (or in the case of psychotherapy studies, superiority to a “psychological placebo” in a study with adequate blinding)
			and
			one or more positive RCT showing superiority to or equivalent efficacy compared with established comparator treatment in a three-arm study with placebo control or in a well-powered non-inferiority trial (only required if such a standard treatment exists)
			In the case of existing negative studies (studies showing non-superiority to placebo or inferiority to comparator treatment), these must be outweighed by at least two more positive studies or a meta-analysis of all available studies shows superiority to placebo and non-inferiority to an established comparator treatment.
			Studies must fulfill established methodological standards^1. The decision is based on the primary efficacy measure.
		↑B	Limited Positive Evidence From Controlled Studies is based on: one or more RCTs showing superiority to placebo (or in the case of psychotherapy studies, superiority to a “psychological placebo”)
			or
			a randomized controlled comparison with a standard treatment without placebo control with a sample size sufficient for a non-inferiority trial
			and
			no negative studies exist
II	Evidence from:	(↑) C	Evidence from Uncontrolled Studies or Case Reports/Expert Opinion
	at least one controlled study without randomisation, or
	at least one other type of quasi-experimental study	C1	Uncontrolled Studies is based on: one or more positive naturalistic open studies (with a minimum of five evaluable patients)
			or
			a comparison with a reference drug with a sample size insufficient for a non-inferiority trial
			and
			no negative controlled studies exist
III	Evidence from non-experimental descriptive studies, such as comparative studies, correlation studies and case–control studies
		C2	Case Reports
			is based on:
			one or more positive case reports
			and
			no negative controlled studies exist
IV	Evidence from expert committee reports or opinions and/or clinical experience of respected authorities	C3	Based on the opinion of experts in the field or clinical experience
		↔ D	Inconsistent Results
			Positive RCTs are outweighed by an approximately equal number of negative studies
		↓ E	Negative Evidence
			The majority of RCTs studies shows non-superiority to placebo (or in the case of psychotherapy studies, superiority to a “psychological placebo”) or inferiority to comparator treatment
		? F	Lack of Evidence
			Adequate studies proving efficacy or non-efficacy are lacking

Eccles M, Mason J. How to develop cost-conscious guidelines. Health Technol Assess 2001; 5: 1–69

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